KEYWORDS soil soil composition mineral particles parent material air water organic matter pore spaces plant litter micro-organisms humus soil profile soil horizon bedrock soil texture soil structure pH value soil moisture soil colour topography weathering erosion humification leaching podzolisation laterisation salinisation calcification zonal soils brown earths latosols intrazonal soils azonal soils soil degredation desertification Sahel overgrazing overcropping deforestation soil conservation Great Green Wall agroforestry bunds zai holes

The composition of a typical soil Composition of soil The composition of a typical soil

Soil profile

Soil texture is usually shown by a soil triangle

Three main soil structures PED TYPE SHAPE DESCRIPTION Crumb This structure is granular. It consists of small rounded grains, like breadcrumbs, that lie loosely on the surface and are easily broken apart. This is the most common type of structure. It is excellent for drainage and air movement. Platy This structure consists of thin, flat particles that often overlap horizontally. It is usually found in clay soils that have been compacted. Platy structure tends to impede the downward movement of water and plant roots through the soil. Blocky This structure consists of cube-shaped particles that fit very tightly together. Blocky structure is most common in the B horizon. It allows for moderate drainage.

The soil pH table is logarithmic

Organic matter is broken down to form humus Humus in soil Organic matter is broken down to form humus

Influences on soil formation Parent material Mineral content Texture Drainage Topography Altitude Gradient Aspect Living organisms Recycling nutrients Aeration and mixing Organic matter Climate Weathering Precipitation Temperature Time Soil thickness The factors that influence soil formation

Organisms influence the structure and fertility of soil Living organisms Organisms influence the structure and fertility of soil

Topography influences the formation of soil

Soil develops slowly over time

Processes of soil formation Soil-forming processes

Soil profile of a podzol soil Podzolisation Soil profile of a podzol soil

Latosol soils get their red colour from iron oxide (rust) Laterisation Latosol soils get their red colour from iron oxide (rust)

A crust of salt may accumulate near the surface Salinisation A crust of salt may accumulate near the surface

The zonal soil most likely to be found in a region Zonal soils The zonal soil most likely to be found in a region

Zonal soils and the climate type they are linked with VEGETATION Latosols Tropical/equatorial Tropical rainforest Aridosols Desert Terra rossa Warm temperature maritime Mediterranean Brown earths Cool temperature maritime Mixed deciduous forest Chernozems Continental Prairies/steppes Podzols Boreal (subarctic) Coniferous forest (taiga) Tundra Zonal soils and the climate type they are linked with

General soil map of Ireland Soils of Ireland General soil map of Ireland

Brown earth soils support a wide range of farming types

Profile of a brown earth soil Brown earth soils support a wide range of farming types

The Sahel and Green Wall The arid land of the Sahel runs east-west across Africa

Precipitation in the Sahel Variations in precipitation over time in the Sahel

Overgrazing in the Sahel Overgrazing has led to soil degradation in the Sahel

Deforestation in the Sahel Charcoal is in demand as a fuel, especially for cooking

Agroforestry in the Sahel Agroforestry is a combination of agriculture and forestry

Soil conservation in the Sahel Constructing bunds in Eritrea

Soil conservation in the Sahel Zai holes are planting pits

Summary chart

Summary chart

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